CPM was proposed by Open Mobile Architecture (OMA) in 2005 to realize interworking of a plurality of message services and provide uniform message services and provide perfect, consistent and convenient message service experience. The CPM converges a plurality of existing message services, comprising Instant Message (IM), Push-To-Talk over Cellular (POC), Mobile E-Email (MEM), Short Messaging Service (SMS), Multimedia Messaging Service (MMS), etc.
The principal service forms of CPM comprise: CMP messages based on a pager-mode, large message mode CPM messages based on a session-mode and other CPM session services based on a session. Before the normal use of these services, users need to register with and log in a CPM system, i.e. usually called “online”.
The large message mode CPM message refers to a CPM message of which the size exceeds the pre-defined limit in the CPM specification formulated by OMA, for example, exceeding the pre-defined limit of 1300 bytes. This large message mode CPM message cannot be directly borne with a Session Initiation Protocol (SIP) message.
The SIP message is used to transmit pager-mode messages between the transmitter's and receiver's CPM Clients and CPM Enablers. When the transmitter terminal needs to transmit a large message mode CPM message, if the size of the message exceeds the limit, then the message cannot be borne with an SIP message.
The CPM service supports CPM pre-defined groups and CPM ad-hoc groups. A CPM user may transmit a CPM pager message to an CPM ad-hoc group or a CPM pre-defined group, but if the size of the message exceeds the limit, then the message cannot be borne with an SIP message.
Paths for transmitting large message mode CPM messages comprise a signaling path and a media path, i.e., signaling is transmitted along a signaling path and media is transmitted along a media path. When a large message mode CPM message is transmitted to a group, a session invite message (INVITE) of the large message mode CPM message is used at first to establish a session between a transmitter CPM client and a controlling function entity, and between the controlling function entity and every receiver CPM client, accomplish media negotiation, and establish a transmission link between the transmitter CPM client and the controlling function entity, and between the controlling function entity and every receiver CPM client. Through the established transmission link, a Message Session Relay Protocol (MSRP) is used to transmit the media content of the large message mode CPM message, i.e. the content of CPM message to the foregoing receiver CPM client.
According to the CPM system framework, at the service level, the signaling path through which CPM transmits large messages needs to pass the transmitter CPM client, a source participation function entity to which the transmitter belongs, the controlling function entity, a destination participation function entity to which the receiver belongs and the receiver CPM client. There are two solutions for the CPM media path: in one solution, a media path is established between end and end without passing the participation function entity and the controlling function entity; and in the other solution, it is required to pass the participation function entity and/or the controlling function entity.
In the current formulation stage of the CPM specification, more manufacturers prefer the solution in which the media interface passes intermediate entities such as the participation function entity. Under this condition, media links i.e., MSRP Multiple Hops transmission needs to be established between the CPM transmitter client and the source participation function entity, between the source participation function entity and the controlling function entity, between the controlling function entity and the destination participation function entity, and between the destination participation function entity and the receiver client, respectively. The large message mode CPM message accomplishes the media negotiation by transmitting a large message session invite message from the transmitter to the receiver, so that every function entity gets the adjacent function entity with which it will establish a link, i.e. acquires the MSRP connection parameters of the entity with which it will establish a link, the MSRP connection parameters comprise IP address, port number and/or Universal Resource Identifier (URI). However, with respect to the transmission of large message mode CPM, currently no solution is available to solve the problem of sectionally establishing an MSRP multiple hops link among respective function entities, thereby establishing a complete MSRP transmission link.